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Abstract:

An illumination system comprising of at least one fast response light
source of each of at least two different colors, and a mechanism for
activating the light sources alternately is disclosed. The illuminations
system generates a train of pulses of that at least two different colors,
the pulse train having a frequency above 350 Hz, a duty cycle in the
range of 5% to 80%, a predefined sequence of pulses of the at least two
different colors within a predefined time period. Furthermore, a method
for synthesizing a light color is provided. The method comprising
providing fast response light sources of a least two different colors,
defining a train of pulses having a frequency above 350 Hz and a duty
cycle in the range of 5% to 80%, defining a time period and an activation
sequence for activating the at least two different colors alternately,
and activating the fast response light sources to emit the train of
pulses according to the time period and the activation sequence.

Claims:

1. An illumination system, comprising: at least one fast response light
source of each of at least two different colors; and a mechanism for
activating said light sources alternately to generate a train of pulses
of said at least two different colors, said pulse train having a
frequency above 350 Hz, a duty cycle in the range of 5% to 80%, a
predefined sequence of pulses of said at least two different colors
within a predefined time period.

2. The illumination system according to claim 1, wherein said mechanism
for activating said light sources includes (i) a pulse power supply for
generating activating pulses to said at least one fast response light
source of each of at least two different colors, and (b) a control unit
for managing said pulse power supply.

3. The illumination system according to claim 1, wherein said fast
response light sources are light emitting diodes.

4. The illumination system according to claim 1, wherein said fast
response light sources are plasma light sources.

5. The illumination system of claim 1, further comprising a
phosphor-based white LED that is activated by said mechanism along with
said fast response light sources.

6. The illumination system of claim 5, wherein said illumination system
has a CRI greater than 90.

7. The illumination system of claim 5, wherein said illumination system
has energy saving gain factor proportional to the ratio of the activating
pulses peak current to cycle average current.

8. The illumination system according to claim 1, wherein said fast
response light sources are grouped in respective arrays and wherein said
arrays of light sources are activated alternately.

9. An electronic device comprising the illumination system of claim 1 as
a display system thereof.

10. The electronic device according to claim 9, wherein said electronic
device is selected from the group consisting of televisions, computers,
cellular phones and electronic game devices.

11. A method for synthesizing a light color, the method comprising:
providing fast response light sources of at least two different colors;
defining a train of pulses having a frequency above 350 Hz and a duty
cycle in the range of 5% to 80%; defining a time period and an activation
sequence for activating said at least two different colors alternately;
and activating said fast response light sources to emit said train of
pulses according to said time period and said activation sequence.

14. The method according to claim 11, wherein said fast response light
sources are grouped in respective arrays and wherein said arrays of light
sources are activated alternately.

15. The method according to claim 11, wherein said train of pulses
provides color information of a display of an electronic device.

16. The method according to claim 11, wherein said electronic device is
selected from the group consisting of televisions, computers, cellular
phones and electronic game devices.

17. The method according to claim 11, further comprising providing a
phosphor-based white LED and activating said phosphor-based white LED
along with the fast response light sources.

18. The method according to claim 17, wherein said synthesized light has
CRI greater than 90.

19. The method according to claim 17, wherein said synthesized light has
an energy saving gain factor proportional to the ratio of the activating
pulses peak current to cycle average current.

Description:

FIELD OF THE INVENTION

[0001] The invention relates generally to light sources, and more
particularly to synthesis of light color with high quality and high
illumination efficacy.

BACKGROUND OF THE INVENTION

[0002] The eye retina consists of a large number of photoreceptor cells
which contain Opsin molecules. Opsin is the universal photoreceptor
molecule of all visual systems. Opsin molecules change their conformation
from a resting state to a signaling state, insensitive to further light
absorption, and return to their initial resting state after some
characteristic time. Due to the Opsin photoreceptor molecules light
absorption cycle, the visual system has a slow response time, and the
retention of the human visual system is exploited for example by the
movies industry where projecting a rapid sequence of pictures creates an
illusion of movement.

[0003] The visual system codes the color of an image using three types of
Opsin molecules that differ in the light wavelength they respond to
optimally (bluish, greenish and reddish Opsin molecules). Accordingly,
the visual system codes the color of an image concurrently.

[0004] White or any other color can be formed by mixing colored lights.
The most common method is to use red, green and blue (RGB) light sources
simultaneously. For example, white color may be produced by several types
of multi-colored light emitting diodes (LEDs) activated simultaneously,
such as di-, tri-, and tetrachromatic LEDs. Several key factors that play
among these different methods include color stability, color rendering
capability, and luminous efficacy. Often higher luminous efficiency
implies lower color rendering, presenting a trade off between the
luminous efficiency and the color rendering. For example, dichromatic
white LEDs have the best luminous efficacy (120 lm/W) but the lowest
color rendering capability. Conversely, tetrachromatic white LEDs have
good color rendering capability, but often have poor luminous efficiency.
Trichromatic white LEDs are in between, having mid values luminous
efficacy (>70 lm/W) and mid values color rendering capability.

[0005] Thus, there is a long felt need to synthesize white light with high
color rendering incex (CRI) and others light colors with high
illumination efficacy using at least two different colors.

SUMMARY OF THE INVENTION

[0006] Accordingly, it is a principal object of the present invention to
overcome the disadvantages of prior art illumination systems. This is
provided for in the present invention by an illumination system
comprising of at least one fast response light source of each of at least
two different colors, and a mechanism for activating the light sources
alternately is disclosed. The illumination system generates a train of
pulses of the at least two different colors, the pulse train having a
frequency above 350 Hz, a duty cycle in the range of 5% to 80%, a
predefined sequence of pulses of the at least two different colors within
a predefined time period.

[0007] Furthermore, a mechanism for activating the light sources that
includes (i) a pulse power supply for generating activating pulses to at
least one fast response light source of each of at least two different
colors, and (b) a control unit for managing the pulse power supply is
provided.

[0009] Furthermore, the illumination system may further comprise a
phosphor-based white LED that is activated by the mechanism along with
the fast response light sources.

[0010] Furthermore, the illumination system may have CRT greater than 90.

[0011] Furthermore, the illumination system may have energy saving gain
factor proportional to the ratio of the activating pulses peak current to
cycle average current.

[0012] Furthermore, the fast response light sources may be grouped in
respective arrays and wherein the arrays of light sources are activated
alternately.

[0013] Furthermore, an electronic device comprising the illumination
system as a display system thereof is provided. The electronic device may
be selected from the group consisting of televisions, computers, cellular
phones and electronic game devices.

[0014] Furthermore, a method for synthesizing a light color is provided.
The method comprising: providing fast response light sources of at least
two different colors, defining a train of pulses having a frequency above
350 Hz and a duty cycle in the range of 5% to 80%, defining a time period
and an activation sequence for activating said at least two different
colors alternately, and activating the fast response light sources to
emit the train of pulses according to the time period and activation
sequence.

[0015] Additional features and advantages of the invention will become
apparent from the following drawings and description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] For a better understanding of the invention and to show how the
same may be carried into effect, reference will now be made, purely by
way of example, to the accompanying drawings in which like numerals
designate corresponding elements or sections throughout.

[0017] With specific reference now to the drawings in detail, it is
stressed that the particulars shown are by way of example and for
purposes of illustrative discussion of the preferred embodiments of the
present invention only, and are presented in the cause of providing what
is believed to be the most useful and readily understood description of
the principles and conceptual aspects of the invention. In this regard,
no attempt is made to show structural details of the invention in more
detail than is necessary for a fundamental understanding of the
invention, the description taken with the drawings making apparent to
those skilled in the art how the several forms of the invention may be
embodied in practice. In the accompanying drawings:

[0018] FIG. 1 illustrates an illumination system, according to embodiments
of the present invention;

[0019]FIG. 2 illustrates a train of pulses, according to embodiments of
the present invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Embodiments of the present invention enable synthesis of white
light with high CRI and any other light colors with high illumination
efficacy using LEDs or other fast response light sources.

[0021] Embodiments of the present invention exploit two important features
of the visual system's Opsin molecules: a. Opsin photoreceptor molecules
absorb light, trigger phototransduction cascade and remain insensitive to
light for relatively long time period, and b. There are three different
Opsin molecule types in the eye retina that code the color of an image.

[0022] According to embodiments of the present invention, the synthesis of
any light color with high illumination efficacy may be achieved by high
frequency (>350 Hz), low duty cycle trains of pulses. The train of
electric current pulses activates fast response light sources of two or
more different colors and has a predefined time period and sequence of
activation of the fast response light sources.

[0023] Before explaining at least one embodiment of the invention in
detail, it is to be understood that the invention is not limited in its
application to the details of construction and the arrangement of the
components set forth in the following description or illustrated in the
drawings. The invention is applicable to other embodiments or of being
practiced or carried out in various ways. Also, it is to be understood
that the phraseology and terminology employed herein is for the purpose
of description and should not be regarded as limiting.

[0024] FIG. 1 illustrates an illumination system, according to embodiments
of the present invention. Illumination system 100 includes a pulse power
supply 110, a control unit 120, fast response light sources 130 of at
least two different colors and an enclosure with at least one transparent
surface 140. Illumination system 100 may be a lamp generating white or
any other color light for indoor or outdoor usage. Illumination system
100 may be used to supply color information to any electronic device
display of, for example, computers, televisions and cellular phones (as
non-limiting examples).

[0025] Illumination system 100 is enclosed in an enclosure with at least
one transparent surface. Pulse power supply 110 generates the activating
trains of pulses to fast response light sources 130 and is managed by
control unit 120. Fast response light sources 130 may be fast response
light sources of at least two different colors such as (in the case of
three different colors) red, green and blue (RGB) color LEDs, or other
types of fast response light sources, such as plasma light sources. Pulse
power supply 110 includes a mechanism for activating fast response light
sources 130 alternately to generate a train of pulses of colored light.
Fast response light sources 130 may be discrete light source units or
arrays of light source units. Different sets of colors, other than the
commonly used RUB, may be used to synthesize light color with high
quality and high illumination efficacy according to embodiments of the
present invention. Fast response light sources like LEDs and plasma
sources turn on and off in less then 5 microseconds. Hence, in the
appended claims, a "fast response" light source is a light source with a
rise time of at most about 5 microseconds and a fall time of at most
about 5 microseconds.

[0027]FIG. 2 illustrates a train of electric current pulses according to
embodiments of the present invention. A train 200 of pulses may have, for
example, a 5 KHz frequency (cycle time of 200 microseconds) and a 10
microsecond pulse width (a 5% duty cycle). Note that the cycle time and
the pulse width recited above are given as an example only and are not
limiting. Any frequency higher than 350 Hz may be used with the present
invention. Note that the first pulse 210 activates a red color LED, the
second pulse 220 activates a green color LED, the third pulse 230
activates a blue color LED and the forth pulse 240 activates again a red
color LED.

[0028] Color rendering index (CRI) is a quantitative measure of the
ability of a light source to reproduce the colors of various objects
faithfully in comparison with an ideal or natural light source. According
to embodiments of the present invention, the overall time period and the
sequence of appearance of the different colored pulses (LED red, green
and blue colors for example) may be changed by a person skilled in the
art such that any desired visual color may be obtained. The synthesized
light absorbed by a human eye may be composed of the three colored pulses
in a sequence in a train of pulses. For example a pulse train period may
be a pulse sequence of 100 high frequency pulses, composed of 37
activations of red color LED, 35 activations of green color LED and 28
activations of blue color LED. The activation of different color LEDs may
be randomly distributed or in a predefined sequence within the pulse
train period. Any color may be synthesized using various high frequency
pulses (>350 Hz), low duty cycle, predefined pulse train period and
predefined sequences of activation of different color LEDs.
Advantageously, the frequency, the duty cycle, the predefined pulse train
period and predefined sequences of activation of different colors light
sources may be defined by persons skilled in the art in order to generate
an energy-saving light source with high illumination efficacy.

[0029] According to embodiments of the present invention, the duty cycle
may be in the range of 5% up to 80% of a cycle time. Due to the low duty
cycle and to the fact that the visual system perceives a high frequency
pulses train as continuous light source, a very high efficacy and energy
saving illumination may be achieved. The average current drawn by the
pulse power supplies in a cycle, IRMS (shown in FIG. 2), is much
lower than the pulse peak current, IPEAK (shown also in FIG. 2). The
ratio of the peak to average currents is a measure of the energy saving
of the illumination system. At low pulses frequency, less than 350 Hz,
the visual system operates as an energy averaging sensor and no power
gain can realized by reducing the pulses duty cycle. At higher pulse
frequency of 100 KHz and more, the visual system operates as a peak
detector responding to the peak light energy as if it is exposed to a
continuous light source with this peak energy, thus enabling significant
energy saving by reducing the pulses duty cycle. Advantageously, persons
skilled in the art may define the pulses cycle time and duty cycle that
will generate an energy saving high illumination efficacy light source
according to embodiments of the present invention.

[0030] Because the visual system synthesizes a series of high frequency
and low duty cycle light pulses with different colors into a colored
continuous light, any color in the visible range may be synthesized by
high frequency, low duty cycle train of pulses with a predefined pulse
train period and predefined sequence of activation of different color
fast response light sources.

[0031] Another prior art way to form white light source involves coating
an LED of blue color with phosphor of different colors. Unfortunately,
these phosphor based white LEDs have medium values CRI (<80).
According to embodiments of the present invention, an improved white
light source with high CRI (>90) may be formed by adding to a Phosphor
based white LED the illumination system described above, where high
frequency, low duty cycle train of pulses with a predefined pulse train
period and predefined sequence of activation are used to activate at
least two different color fast response light sources.

[0032] Furthermore, according to embodiment of the present invention, the
improved white light source described above may have both high CRI
(>90) and high efficacy illumination when activated by a train of high
frequency pulses (500 KHz for example) and low duty cycle (10% for
example). The improved white light source described above may have energy
saving gain proportional to the ratio of the activating pulses peak
current to cycle average current.

[0033] Advantageously, blue, green and red LEDs are fast response light
sources that may be used to construct any light color with high CRI and
energy saving high illumination efficacy according to embodiments of the
present invention.

[0034] Advantageously, other fast response light sources such as plasma
light sources may be used according to embodiments of the present
invention.

[0035] In summary, illumination systems as described above overcome the
difficulties and limitations of the prior art illumination systems by
constructing an improved white light with high CRI and any other color
with energy-saving high illumination efficacy using a high frequency and
low duty cycle pulse train, with a predefined pulse train period and
predefined sequences of activation of different color fast response light
sources.

[0036] It is appreciated that certain features of the invention, which
are, for clarity, described in the context of separate embodiments, may
also be provided in combination in a single embodiment. Conversely,
various features of the invention which are, for brevity, described in
the context of a single embodiment, may also be provided separately or in
any suitable sub-combination.

[0037] Unless otherwise defined, all technical and scientific terms used
herein have the same meanings as are commonly understood by one of
ordinary skill in the art to which this invention belongs. Although
methods similar or equivalent to those described herein can be used in
the practice or testing of the present invention, suitable methods are
described herein.

[0038] All publications, patent applications, patents, and other
references mentioned herein are incorporated by reference in their
entirety. In case of conflict, the patent specification, including
definitions, will prevail. In addition, the materials, methods, and
examples are illustrative only and not intended to be limiting.

[0039] It will be appreciated by persons skilled in the art that the
present invention is not limited to what has been particularly shown and
described hereinabove. Rather the scope of the present invention is
defined by the appended claims and includes both combinations and
sub-combinations of the various features described hereinabove as well as
variations and modifications thereof, which would occur to persons
skilled in the art upon reading the foregoing description.